In a recent study published in Scientific Reports, researchers investigate the association between cannabis use and first open-angle glaucoma (POAG), a severe non-communicable eye disease.

Study: Cannabis use and the chance of primary open-angle glaucoma: A Mendelian randomization study. Image Credit: PeopleImages.com – Yuri A / Shutterstock.com

Glaucoma and its association with cannabis

Glaucoma is an umbrella term used to explain eye diseases characterised by irreversible damage to the optic nerve. The condition and its symptoms can progress slowly, thus causing many patients to be unaware of its presence.

The one accurate diagnostic approach for glaucoma is a comprehensive dilated eye exam. Despite its silence and slow progression, glaucoma is chargeable for greater than 78 million everlasting losses of vision globally, thereby making it the leading reason for blindness on the planet today.

Researchers estimate that glaucoma cases remain on the rise, with its prevalence estimated to extend to over 100 million by the yr 2040. Probably the most common glaucoma subtype is primary open-angle glaucoma (POAG), which is brought on by excessive long-term intraocular pressure (IOP). IOP is a modifiable risk factor, with eye drops relieving the condition and subsequently delaying glaucoma onset; nonetheless, most sources of the IOP remain unknown.

Studies over the past decade have identified ocular uncomfortable side effects related to persistent eye drop use. This has led many patients and their medical advisors to make a choice from potentially faster-progressing glaucoma or a distinct visual disease. Consequently, the seek for novel treatment modalities to enhance IOP outcomes has been the main focus of recent research.

Cannabinoids, the bioactive compounds derived from cannabis plants, appear to mitigate IOP. Nevertheless, most studies on the potential therapeutic effects of cannabinoids for IOP were short-term and comprised small study cohorts, thus limiting the reliability of those results. Moreover, most types of cannabis consumption involve the usage of tobacco as a ‘mixer,’ thus making studies into their individual effects difficult.

Concerning the study

In the current study, researchers collated data from multiple medical repositories, including the UK Biobank, 23andMe, and the International Cannabis Consortium. The dataset comprised genome-wide association study (GWAS) summary data from 184,765 individuals with European ancestry, making it probably the most extensive study of cannabis users so far. Inclusion criteria were the self-reported lifetime use of cannabis, with data assorted and corrected from sex, ancestry, age, and approach to genotyping.

Moreover, data from a previous meta-analysis conducted by the Lundbeck Foundation Initiative for Integrative Psychiatric Research (iPSYCH), deCODE, and the Psychiatric Genomics Consortium Substance Use Disorders working group were added to the dataset. This dataset comprised 17,068 cannabis users with dependence or abuse symptoms, in addition to 357,219 controls.

Mendelian randomization (MR) is a statistical model of genetic data processing that will present an answer to this ongoing conundrum. Researchers used MR to discover single nucleotide polymorphisms (SNPs) related to lifetime cannabis use, abuse, or dependence, following which they calculated the quantity of phenotypic variance explained by IOP. The MR_Steiger directionality test was used to check causality and eliminate SNPs strongly correlated with POAG but weakly related to cannabis consumption.

Five SNPs related to lifetime cannabis use and eleven SNPs related to cannabis use disorder were chosen in the first evaluation, while 267 and 157 SNPs related to lifetime cannabis and cannabis use disorder, respectively, were chosen within the secondary evaluation.”

Study findings

Of the over 550,000 individuals sampled, about 16,000 were diagnosed with POAG. Nevertheless, while the meta-analyses identified SNPs related to cannabis use or cannabis disorder, these SNPs didn’t overlap with SNPs related to POAG.

Statistical analyses revealed that the chances ratios (ORs) of POAG in users as in comparison with never users was 1.03, which is statistically insignificant. Adjustments for sex, age, ancestry, and genotyping didn’t alter these results.

These findings highlight that cannabis use, and even abuse over a lifetime, doesn’t end in IOP and thereby contributes to POAG. While the study does have inherent limitations as a result of its binary nature of only considering users or never users, it was able to ascertain a scarcity of an association between cannabis use and any type of glaucoma.